CHIME dating and age mapping of monazite in granulites and paragneisses from the Hwacheon area, Korea: implications for correlations with Chinese cratons
CHIME dating and age mapping of monazite in granulites and paragneisses from the Hwacheon area, Korea: implications for correlations with Chinese cratons
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DOI：
10.1007/s12303-009-0027-z
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发表时间：
2009-11
影响因子：
1.2
通讯作者：
Kazuhiro Suzuki
中科院分区：
文献类型：
--
作者：
Kazuhiro Suzuki
位于朝鲜半岛京畿海沟北方的华川地区的基底由麻粒岩和片麻岩杂岩组成，它们被广泛的糜棱岩带分隔。远离糜棱岩带的麻粒岩除了沿沿着石榴子石晶界生长的黑云母外，几乎没有退化叠印的证据。独居石颗粒封闭在石榴石显示核心边缘减少Y，和那些在基质中显示外围富集Y低Y内部。类似地，石榴石晶粒从核心到边缘Y减少，外围Y富集，这可以归因于早期峰值石榴石生长和生长后的修改，分别。代表独居石生长阶段的三个化学结构域没有显示出可检测的年龄差异，共同得出CHIME年龄为1868 ± 24 Ma。糜棱岩带附近的麻粒岩显示生长的堇青石和黑云母聚集体周围的石榴石颗粒，并产生二叠纪-三叠纪独居石域上和内主要是古元古代独居石颗粒。糜棱岩化麻粒岩具有变质叠加特征，其特征是在约1000 ℃时硅线石和钾长石组合的生长。241 Ma，韧性剪切作用之后。片麻岩杂岩中的泥质片麻岩含有新元古代碎屑核锆石颗粒和独居石颗粒，变质年龄为约1000年。245 Ma.地质学、岩石学和年代学证据表明，在合并之前，两个地壳域的演化历史不同。京畿道二叠纪-三叠纪副片麻岩和糜棱岩的广泛产出可以解释为华南陆块变质上地壳的拆离作用，该陆块在约2000年逆冲到古元古代麻粒岩杂岩之上。241 Ma，苏禄造山运动时期。后者上的二叠-三叠纪变质叠印是来自热外来体的接触变质作用。
The basement of the Hwacheon area in the northern part of the Gyeonggi massif in the Korean Peninsula comprises granulite and gneiss complexes that are separated by an extensive mylonite zone. Granulites distant from the mylonite zone show little evidence of a retrograde overprint beyond minor growth of biotite along garnet grain boundaries. Monazite grains enclosed in garnet show a core to rim decrease in Y, and those in the matrix show a peripheral enrichment of Y on low-Y interiors. Similarly, garnet grains decrease in Y from core to rim, with peripheral Yenrichment, which can be attributed to early to peak garnet growth and post-growth modification, respectively. The three chemical domains representing stages of monazite growth show no detectable age difference, together yielding a CHIME age of 1868 ± 24 Ma. Granulites near the mylonite zone show growth of cordierite and biotite aggregates around garnet grains, and yield Permo-Triassic monazite domains on and within predominantly Paleoproterozoic monazite grains. Mylonitized granulites have a metamorphic overprint characterized by the growth of the sillimanite and K-feldsper assemblage at ca. 241 Ma, subsequent to ductile shearing. Pelitic gneisses in the gneiss complex contain zircon grains with Neoproterozoic detrital cores and monazite grains with unequivocal metamorphic ages of ca. 245 Ma. Geological, petrological and chronological evidence suggests differing evolutional histories between two crustal domains prior to amalgamation. The widespread occurrence of Permo-Triassic paragneisses and mylonites in the Gyeonggi massif can be explained by detachment of the metamorphosed upper crust of the South China block, which was thrust over the Paleoproterozoic granulite complex at ca. 241 Ma during the Sulu orogeny. Permo-Triassic metamorphic overprints on the latter are attributed to contact metamorphism from the hot allochthon.